The Commission plans to order Google to stop offering payments or discounted license fees to smartphone makers for putting its search engine and app store on their phones systems based on Android.

If Google does not stop, the company faces a fine "at a level which will be sufficient to ensure deterrence," Reuters quoted the document as saying. The fine will be calculated based on the duration of the anticompetitive practices -- from January 2011 to the present -- and the revenue they generate, including that from AdWords clicks by European users, Google Search product queries, Play Store apps purchase and AdMob in-app advertisements, said the document sent to complainants last week.

A spokesman for Fairsearch, a group lobbying for competition in online and mobile search, said the organization had no immediate comment on the report. Google and the European Commission did not immediately respond to requests for comment.

Competition Commissioner Margrethe Vestager said in April that she is concerned that Google, by forcing phone makers to exclusively use certain of its own apps, is excluding rival app developers from a key way to reach new customers: pre-loading them on new smartphones.